The long-term goal of the proposed research is an understanding of the pathways of sesquiterpene construction in plants, their significance to modern plants and to their ancient predecessors. Our earlier studies reveal that certain taxa low in the phylogeny of plants (liverworts as an example) produce sesquiterpenes strictly enantiomeric to those of higher plants. We propose that this change is of ecological significance. The methods to be deployed in this study of sesquiterpene biogenesis are: comparative oil composition studies in primitive phyla, the chemical simulation of biogenesis, and radiotracer incorporation in the in vivo synthetic process of liverworts. The chemical simulation studies should reveal the energetics of the reactions proposed as biosynthetic pathways and the points at which enzymic control is essential for economy (yield maximization or selection between alternative rearrangements) and stereospecificity. These critical points are then the foci of chemotaxonomic studies. The chemotaxonomic studies should clarify the point in plant phylogeny at which sesquiterpene inversion occurred through congeneric occurrence patterns and absolute stereochemistry correlations. Further we expect these studies to support the biosynthetic proposals by providing occasion for the isolation of "missing links." The latter are particularly important since the relative merits of hypotheses are best judged on their predictive value. The ultimate proof of biogenetic pathways is the demonstration of conversion in vivo using labeled precursors. To this end we will optimize incorporation of C14-acetate, C14-mevalonate, and H3-mevalonate in growing liverworts. The labeled sesquiterpenes will be systematically degraded in order to establish the location of the labeled atoms.